1. Field of the Invention
The present invention relates to lens driving devices, and in particular to a lens driving device that is suitably mounted on a small camera or the like to provide auto-focus functionality.
2. Description of the Related Art
Conventionally, various lens driving devices are mounted on optical devices. As known examples of such lens driving devices, there are motor driven actuators utilizing a stepping motor, piezoelectric actuators utilizing piezoelectric distortion when an electric field is applied to a crystalline body, and electromagnetic actuators utilizing a voice coil that are adopted for loudspeakers or the like.
For example, a voice coil lens driving device is mounted on a camera in order to realize auto-focus functionality. With the voice coil lens driving device, a coil is attached to a holder that holds a lens, and a magnet is attached to a base. Application of current to the coil produces electromagnetic driving force. The electromagnetic driving force drives the holder along a direction of an optical axis of the lens.
With the voice coil lens driving device, a spring member that supports the holder may also be used for supplying power to the coil. With this configuration, a wire for power supply to the coil does not have to be drawn from the holder. As a result, undesirable vibration or tensile force may not be applied to the wiring when driving the lens. Therefore, it is possible to suppress a problem that such vibration or tensile force may damage the wiring may be suppressed. On the other hand, however, this configuration has a problem that yield ratio at production of actuators is easily reduced because the configuration of the spring is complicated.
The above problem may be eliminated by attaching the magnet to the holder and the coil to the base. With this configuration, the wiring to the holder is not necessary in the first place, and the damage to the wiring and the like when driving the lens fails to occur. Further, it is possible to simplify the configuration.
However, because a magnet is generally heavier than a coil, attaching a magnet to the holder makes the movement of the holder and the lens difficult. In particular, when the holder is driven in a vertical direction, a difference between downward movement and upward movement is easily generated due to an influence of gravitational force. For example, there may be differences in speeds when starting to move and drive responses between downward movement and upward movement (hereinafter, such a difference in the movement is referred to as a “drive difference”). Therefore, with this configuration, a smooth lens driving may not be realized when moving the holder in a vertical direction.